1. Field of the Invention
This invention relates to the field of step-change automatic transmissions for motor vehicles, particularly to such transmissions whose principal axis is arranged transversely in a vehicle.
2. Description of the Prior Art
Various kinematic arrangements that minimize the number of friction clutches and brakes in a multiple-speed automatic transmissions able to produce six or more forward speed ratios are known. For example, U.S. Pat. No. 5,106,352 describes a gear arrangement wherein a first planetary gear set produces an output speed that is reduced relative to the speed of an input shaft. This output is selectively driveably connected to a planetary gear set of the Ravigneaux type, which is also selectively driveable connectable to the input shaft. This arrangement results in six forward speeds using three clutches and two brakes, a compact design suitable for transversely directed transmissions for use in front wheel drive vehicles.
U.S. Pat. Nos. 6,110,069 and 6,120,410 describe various techniques for reducing the axial length of such transmissions so that they package in a confined space limited by the size of the engine compartment. U.S. Pat. No. 6,135,912 describes a gear train in which seal rings are arranged in a hydraulic path for applying hydraulic pressure to the clutches and brakes and for sealing at a position where members rotate. Relatively large sliding resistance occurs between members that rotate relative to each other. If the number of seal rings increases, the rotational resistance of corresponding rotational members increases and power loss increases. Grooves, in which seal rings are arranged, need high accuracy because the seal rings contact the grooves to seal the oil. Therefore, certain surfaces contacted by the seals need to be hardened to minimize wear. These actions increase manufacturing time and cost. Therefore it is desirable to decrease the number of such dynamic seals in an automatic transaxle.
In the gear train of U.S. Pat. No. 5,106,352, there are two input torque delivery paths. Output from the torque converter drives a planetary gear set on one side, and the output from the torque converter is decelerated through a reduction planetary gear on an opposite side. There is need there for many seal rings because the connections among the hydraulic paths that apply hydraulic pressure from the transmission case to the hydraulic servos are complicated and the hydraulic paths pass many times between rotating members.
Generally, hydraulic pressure is applied to a hydraulic servo of each clutch from a front end wall portion and a rear end wall portion of the transmission case. Arranging a center support on the middle portion of the transmission case and applying hydraulic pressure from the center support simplify the hydraulic paths. In this case, the number of seal rings is reduced. However, in such a case, the center support is located in the shift mechanism. The number of parts is increased and costs increase. Therefore, it is desirable to simplify the hydraulic paths.